﻿#include "WizLockedFile.h"
#include <string.h>
#include <errno.h>
#ifdef Q_OS_WIN
#include <qt_windows.h>
#include <QtCore/QFileInfo>
#else
#include <unistd.h>
#endif
#include <fcntl.h>

/*!
    \class CWizLockedFile

    \brief The CWizLockedFile class extends QFile with advisory locking functions.

    A file may be locked in read or write mode. Multiple instances of
    \e CWizLockedFile, created in multiple processes running on the same
    machine, may have a file locked in read mode. Exactly one instance
    may have it locked in write mode. A read and a write lock cannot
    exist simultaneously on the same file.

    The file locks are advisory. This means that nothing prevents
    another process from manipulating a locked file using QFile or
    file system functions offered by the OS. Serialization is only
    guaranteed if all processes that access the file use
    CWizLockedFile. Also, while holding a lock on a file, a process
    must not open the same file again (through any API), or locks
    can be unexpectedly lost.

    The lock provided by an instance of \e CWizLockedFile is released
    whenever the program terminates. This is true even when the
    program crashes and no destructors are called.
*/

/*! \enum CWizLockedFile::LockMode

    This enum describes the available lock modes.

    \value ReadLock A read lock.
    \value WriteLock A write lock.
    \value NoLock Neither a read lock nor a write lock.
*/

/*!
    Constructs an unlocked \e CWizLockedFile object. This constructor behaves in the same way
    as \e QFile::QFile().

    \sa QFile::QFile()
*/
WizLockedFile::WizLockedFile()
    : QFile()
{
#ifdef Q_OS_WIN
    m_semaphore_hnd = 0;
    m_mutex_hnd = 0;
#endif
    m_lock_mode = NoLock;
}

/*!
    Constructs an unlocked CWizLockedFile object with file \a name. This constructor behaves in
    the same way as \e QFile::QFile(const QString&).

    \sa QFile::QFile()
*/
WizLockedFile::WizLockedFile(const QString &name)
    : QFile(name)
{
#ifdef Q_OS_WIN
    m_semaphore_hnd = 0;
    m_mutex_hnd = 0;
#endif
    m_lock_mode = NoLock;
}


/*!
    Returns \e true if this object has a in read or write lock;
    otherwise returns \e false.

    \sa lockMode()
*/
bool WizLockedFile::isLocked() const
{
    return m_lock_mode != NoLock;
}

/*!
    Returns the type of lock currently held by this object, or \e CWizLockedFile::NoLock.

    \sa isLocked()
*/
WizLockedFile::LockMode WizLockedFile::lockMode() const
{
    return m_lock_mode;
}


#ifdef Q_OS_WIN

#define SEMAPHORE_PREFIX "QtLockedFile semaphore "
#define MUTEX_PREFIX "QtLockedFile mutex "
#define SEMAPHORE_MAX 100

static QString errorCodeToString(DWORD errorCode)
{
    QString result;
    char *data = 0;
    FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                    0, errorCode, 0,
                    (char*)&data, 0, 0);
    result = QString::fromLocal8Bit(data);
    if (data != 0)
        LocalFree(data);

    if (result.endsWith("\n"))
        result.truncate(result.length() - 1);

    return result;
}

bool WizLockedFile::lock(LockMode mode, bool block)
{
    if (!isOpen()) {
        qWarning("QtLockedFile::lock(): file is not opened");
        return false;
    }

    if (mode == m_lock_mode)
        return true;

    if (m_lock_mode != 0)
        unlock();

    if (m_semaphore_hnd == 0) {
        QFileInfo fi(*this);
        QString sem_name = QString::fromLatin1(SEMAPHORE_PREFIX)
                           + fi.absoluteFilePath().toLower();

            m_semaphore_hnd = CreateSemaphoreW(0, SEMAPHORE_MAX, SEMAPHORE_MAX,
                                               (TCHAR*)sem_name.utf16());

        if (m_semaphore_hnd == 0) {
            qWarning("QtLockedFile::lock(): CreateSemaphore: %s",
                     errorCodeToString(GetLastError()).toLatin1().constData());
            return false;
        }
    }

    bool gotMutex = false;
    int decrement;
    if (mode == ReadLock) {
        decrement = 1;
    } else {
        decrement = SEMAPHORE_MAX;
        if (m_mutex_hnd == 0) {
            QFileInfo fi(*this);
            QString mut_name = QString::fromLatin1(MUTEX_PREFIX)
                               + fi.absoluteFilePath().toLower();
                    m_mutex_hnd = CreateMutexW(NULL, FALSE, (TCHAR*)mut_name.utf16());

            if (m_mutex_hnd == 0) {
                qWarning("QtLockedFile::lock(): CreateMutex: %s",
                         errorCodeToString(GetLastError()).toLatin1().constData());
                return false;
            }
        }
        DWORD res = WaitForSingleObject(m_mutex_hnd, block ? INFINITE : 0);
        if (res == WAIT_TIMEOUT)
            return false;
        if (res == WAIT_FAILED) {
            qWarning("QtLockedFile::lock(): WaitForSingleObject (mutex): %s",
                     errorCodeToString(GetLastError()).toLatin1().constData());
            return false;
        }
        gotMutex = true;
    }

    for (int i = 0; i < decrement; ++i) {
        DWORD res = WaitForSingleObject(m_semaphore_hnd, block ? INFINITE : 0);
        if (res == WAIT_TIMEOUT) {
            if (i) {
                // A failed nonblocking rw locking. Undo changes to semaphore.
                if (ReleaseSemaphore(m_semaphore_hnd, i, NULL) == 0) {
                    qWarning("QtLockedFile::unlock(): ReleaseSemaphore: %s",
                             errorCodeToString(GetLastError()).toLatin1().constData());
                    // Fall through
                }
            }
            if (gotMutex)
                ReleaseMutex(m_mutex_hnd);
            return false;
    }
        if (res != WAIT_OBJECT_0) {
            if (gotMutex)
                ReleaseMutex(m_mutex_hnd);
            qWarning("QtLockedFile::lock(): WaitForSingleObject (semaphore): %s",
                        errorCodeToString(GetLastError()).toLatin1().constData());
            return false;
        }
    }

    m_lock_mode = mode;
    if (gotMutex)
        ReleaseMutex(m_mutex_hnd);
    return true;
}

bool WizLockedFile::unlock()
{
    if (!isOpen()) {
        qWarning("QtLockedFile::unlock(): file is not opened");
        return false;
    }

    if (!isLocked())
        return true;

    int increment;
    if (m_lock_mode == ReadLock)
        increment = 1;
    else
        increment = SEMAPHORE_MAX;

    DWORD ret = ReleaseSemaphore(m_semaphore_hnd, increment, 0);
    if (ret == 0) {
        qWarning("QtLockedFile::unlock(): ReleaseSemaphore: %s",
                    errorCodeToString(GetLastError()).toLatin1().constData());
        return false;
    }

    m_lock_mode = WizLockedFile::NoLock;
    return true;
}

WizLockedFile::~WizLockedFile()
{
    if (isOpen())
        unlock();
    if (m_mutex_hnd != 0) {
        DWORD ret = CloseHandle(m_mutex_hnd);
        if (ret == 0) {
            qWarning("QtLockedFile::~QtLockedFile(): CloseHandle (mutex): %s",
                        errorCodeToString(GetLastError()).toLatin1().constData());
        }
        m_mutex_hnd = 0;
    }
    if (m_semaphore_hnd != 0) {
        DWORD ret = CloseHandle(m_semaphore_hnd);
        if (ret == 0) {
            qWarning("QtLockedFile::~QtLockedFile(): CloseHandle (semaphore): %s",
                        errorCodeToString(GetLastError()).toLatin1().constData());
        }
        m_semaphore_hnd = 0;
    }
}
#else


/*!
    \fn bool CWizLockedFile::lock(LockMode mode, bool block = true)

    Obtains a lock of type \a mode.

    If \a block is true, this
    function will block until the lock is acquired. If \a block is
    false, this function returns \e false immediately if the lock cannot
    be acquired.

    If this object already has a lock of type \a mode, this function returns \e true immediately. If this object has a lock of a different type than \a mode, the lock
    is first released and then a new lock is obtained.

    This function returns \e true if, after it executes, the file is locked by this object,
    and \e false otherwise.

    \sa unlock(), isLocked(), lockMode()
*/

/*!
    \fn bool CWizLockedFile::unlock()

    Releases a lock.

    If the object has no lock, this function returns immediately.

    This function returns \e true if, after it executes, the file is not locked by
    this object, and \e false otherwise.

    \sa lock(), isLocked(), lockMode()
*/

/*!
    \fn CWizLockedFile::~CWizLockedFile()

    Destroys the \e CWizLockedFile object. If any locks were held, they are released.
*/



bool WizLockedFile::lock(LockMode mode, bool block)
{
    if (!isOpen()) {
        qWarning("CWizLockedFile::lock(): file is not opened");
        return false;
    }

    if (mode == NoLock)
        return unlock();

    if (mode == m_lock_mode)
        return true;

    if (m_lock_mode != NoLock)
        unlock();

    struct flock fl;
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;
    fl.l_len = 0;
    fl.l_type = (mode == ReadLock) ? F_RDLCK : F_WRLCK;
    int cmd = block ? F_SETLKW : F_SETLK;
    int ret = fcntl(handle(), cmd, &fl);

    if (ret == -1) {
        if (errno != EINTR && errno != EAGAIN)
            qWarning("CWizLockedFile::lock(): fcntl: %s", strerror(errno));
        return false;
    }


    m_lock_mode = mode;
    return true;
}


bool WizLockedFile::unlock()
{
    if (!isOpen()) {
        qWarning("CWizLockedFile::unlock(): file is not opened");
        return false;
    }

    if (!isLocked())
        return true;

    struct flock fl;
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;
    fl.l_len = 0;
    fl.l_type = F_UNLCK;
    int ret = fcntl(handle(), F_SETLKW, &fl);

    if (ret == -1) {
        qWarning("CWizLockedFile::lock(): fcntl: %s", strerror(errno));
        return false;
    }

    m_lock_mode = NoLock;
    remove();
    return true;
}

WizLockedFile::~WizLockedFile()
{
    if (isOpen())
        unlock();
}
#endif
